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# 0646. Maximum Length of Pair Chain

<https://leetcode.com/problems/maximum-length-of-pair-chain>

## Description

You are given an array of `n` pairs `pairs` where `pairs[i] = [lefti, righti]` and `lefti < righti`.

A pair `p2 = [c, d]` **follows** a pair `p1 = [a, b]` if `b < c`. A **chain** of pairs can be formed in this fashion.

Return *the length longest chain which can be formed*.

You do not need to use up all the given intervals. You can select pairs in any order.

**Example 1:**

```
**Input:** pairs = [[1,2],[2,3],[3,4]]
**Output:** 2
**Explanation:** The longest chain is [1,2] -> [3,4].
```

**Example 2:**

```
**Input:** pairs = [[1,2],[7,8],[4,5]]
**Output:** 3
**Explanation:** The longest chain is [1,2] -> [4,5] -> [7,8].
```

**Constraints:**

* `n == pairs.length`
* `1 <= n <= 1000`
* `-1000 <= lefti < righti <= 1000`

## ac

```java
```